When you update the kernel and your program stops working, there are two possibilities: 1) it's a kernel bug; there is a regression in the kernel's documented

When you update the kernel and your program stops working, there are two possibilities: 1) it's a kernel bug; there is a regression in the kernel's documented behaviour 2) it's a bug in your tool because it took advantage of undefined or undocumented behaviour The bisect found exactly the right patch series, but bisect can only answer the question 'when did it stop working', not 'why'. You can read about many instances of 2) on Raymond Chen's blog The Old New Thing.